bradycardia

What is Bradycardia

The term bradycardia indicates the descent of the heart rate below the normal range for the reference population (drop greater than two standard deviations of the mean).

In adults, it is called bradycardia when the heart rate (CF) is less than 60 beats per minute (bpm). This condition is further divided into:

mild bradycardia (CF between 50 and 59 bpm):
moderate bradycardia (CF between 40 and 49 bpm);
severe bradycardia (HR less than 40 bpm).

Even in the latter case, however, bradycardia may be completely devoid of pathological significance; just think that the heart rate of some professional cyclists - detected in the morning after the alarm - is around 30 bpm (Miguel Indurain recorded 28, Marco Pantani 34-36), while during the dive a trained diver can also get off below this threshold.

Symptoms

In general, therefore, bradycardia is considered absolutely physiological in young and trained individuals.

The condition assumes pathological and potentially dangerous connotations, when it compromises the normal blood supply to the districts of the body, making it insufficient with respect to the metabolic demands. All this accounts for the symptoms typically associated with pathological bradycardia, including dizziness, dyspnoea, fatigue / tiredness, syncope, confusion, chest pain, hypotension and sleep and memory disorders. The same symptoms are also recorded in newborns and very young children (less than a year old), where, however, bradycardia can occur at frequencies below 100 bpm (normally around 120-160 beats per minute, compared to 60 -100 of adults).

Causes

Most of the time bradycardia is a symptom of a problem in the electrical system of the heart.

The Electrical System of the Heart

Inside the right atrium we find the so-called "sinus node" (or sino-atrial node), a natural pacemaker from which the electrical stimuli originate which are subsequently transmitted to the muscle tissue of the atria, causing its activation with consequent atrial contraction and passage of blood in the ventricles.

The electrical impulses originating from the atrial sinus node arrive up to a group of specialized cells, which together form the so-called atrioventricular node, a sort of relay that transmits the electrical signal to another group of cells, called His bundle, which in turn it leads the impulse from the atrioventricular node to the two ventricles. When the electrical stimulus reaches the ventricles, they contract and pump blood into the pulmonary circulation (right ventricle) and into the systemic one (left ventricle).

Cardiac arrhythmias

In the event that an anomaly occurs in one of the various components of the electrical system of the heart, more or less severe arrhythmias may appear, associated or not with bradycardia. Most often the problem occurs at the level of the sinoatrial node, with a decrease in its discharge frequency; in these cases we speak of sinus bradycardia . In other circumstances, the reduced heart rate is due to failure to transmit electrical signals to the ventricles; in these cases we speak of an atrioventricular block, which can have different stages of gravity.

Other Cardiovascular Diseases

Bradycardia can also be caused by ischemic heart disease, myocardial infarction and more generally by degeneration of cardiac tissue; in this sense the main risk factors are represented by advanced age, hypercholesterolemia, hypertension, smoking, alcoholism and excessive stress and anxiety. In other cases degeneration can be linked to infectious processes, such as endocarditis and myocarditis.

Other Possible Causes

Bradycardia can also be the consequence of abnormalities external to the heart, linked - for example - to the abuse of certain drugs, to the use of particular drugs (such as digoxin, beta-blockers and antiarrhythmics, all medicines responsible for iatrogenic bradycardia), to hypothyroidism, to electrolytic alterations (for example an excess of potassium in the blood - hyperpotassemia), to obstructive jaundice and to liver degenerative diseases.

Diagnosis

The most important diagnostic tool is the electrocardiogram, which uses small electrical sensors, connected to the chest and arms, to record the electrical impulses of the heart and their conduction. The exam can be conducted at rest, under stress and in other stress conditions, or for extended periods of time using portable devices.

Special blood tests may be necessary to investigate the presence of underlying diseases, such as hypothyroidism or hyperkalaemia, potentially responsible for bradycardia.